Fluid bed processing systems and methods can be used in a variety of different applications. For example, fluid bed processing systems and methods can be used to dry wet particles for further processing or discharge. Fluid bed processing systems and methods can also be used to coat particles by building identifiable layers evenly over an identified core. Further, fluid bed processing systems and methods can be used to granulate particles into larger aggregates in which the original particles can still be identified in the aggregates.
In fluid bed processing systems and methods, particles to be processed are loaded into a product chamber and are then fluidized into an expansion chamber. If the particles are going to be coated or granulated, a solution is sprayed onto the particles. With the solution, either layers are coated on the particles or the particles begin to aggregate together to form larger particles. The particles dry as they descend down in the expansion chamber and then are blown back up. This up and down process continues until the processing is completed and then the particles are discharged from the product chamber. Different systems and methods have been developed to discharge particles, but each has its own limitations.
For example, some systems, such as the one disclosed in U.S. Pat. No. 4,354,450 to Nagahama et al., which is herein incorporated by reference, use a discharge tube adjacent a lower end of the fluid bed processing system. Although these discharge tubes work, the outlet passages they provide are too small to quickly remove particles from the container of the fluid bed processing system. As a result, the increased time required for discharging the particles decreases the overall production throughput of the fluid bed processing system. The small size for these discharge tubes also makes them more prone to clogging and thus leads to even more down time.
Other systems, such as the one disclosed in U.S. Pat. No. 5,115,578 to Basten which is herein incorporated by reference, have a blower system with a bottom fluidizing screen which is seated against a bottom opening of a container. The bottom screen supports product in the container and can be lowered away from the bottom to permit discharge of the product. Although this system works, it has a number of drawbacks. For example, the weight of the product resting on the bottom screen can be quite large. As a result, these systems need large and expensive lift assemblies to be able to raise and lower the bottom screen and blower away from the container. These weight concerns limit the amount of product which can be loaded into the container for fluid bed processing and thus limit overall production throughput. Another problem is that due to the large weight on the bottom screen over time it may become misaligned with the opening in the bottom of the container resulting in unwanted seepage and jamming.